Card shuffling machine failure

Breaking from his usually routine of winning at everything, [Glacial Wanderer] has posted one of his projects that didn’t actually work. It’s a Rube Goldberg style card shuffling machine. He wanted something that was visually interesting while still randomizing the cards. A blower would be mounted to the top to mix the cards similar to a lottery ball machine. The cards would then drop into a chute that would make sure all of the cards were oriented correctly before being presented to the user. After building the first prototype, several problems were apparent. The first of which was the fan not being strong enough. His interest was waning and it looked like the time he’d have to invest in fixes was growing quickly, so he decided to cut his loses. He still posted about the prototype in hopes that it could help someone else exploring this sort of machine. A video of the mechanism can be found below.

Just saw the second pic on your site of the exhaust ports for the fan. similar to what I asked in the previous comment, could the number of exhaust ports be reduced allowing the air to compress a bit in the chamber? give it a little more force when it comes out. You could simply tape most of the ports from the inside, and through trial and error determine the ideal port amount/pattern.

If there’s enough of a contrast difference between the front and back of the card a simple CdS cell and comparator might even work. If you had a way of reliably checking the same spot on every card you could pick an area near the edge that’s always white on the face side.

I didn’t expect many people to read this post since it didn’t work so I didn’t do a very thorough writeup. Let me list the problems I saw and make some comments.

1) I claimed that the fan was underpowered. This isn’t entirely true. If the fan moved 500 cubic feet of air a minute as advertised I’d have over 30 mph wind and that would be more than enough to blow the cards around. The problem is that airflow is restricted at certain points. One of those is the is the vent. I did try taping up some of the holes and it did not help. I actually found that removing the vent entirely gave the best performance, but it was still not good enough. I think an aerospace engineer could calculate why the observed airflow is so much less the theoretical max, but I can’t. All I know is I was hoping for 10%-20% drop and I’m probably seeing 70-80%. As it stands the cards get blown around as long as they are perpendicular to the airflow they get blown around, but if they turn sideways they fall and get stuck at the bottom. One person on my website suggested using compressed air and I like that idea, but it would increase the cost. I also think replacing the fan entirely with a spinning plexiglass cube might be a good solution.

2) I completely agree with those above that a webcam could easily detect if a card is upside down. However, I was planning to go a cheaper route. I was planning to use just an Arduino and no PC. I know if I put a black dot on one side of the cards I could reliably detect that dot with IR sensor. I think I could have also probably used a specialized clear IR paint. Another option would be to find a deck of cards that allowed the IR sensor to work without modifying the cards. I am pretty sure this problem is easy to solve so I was saving it to last.

3) Cards sometimes randomly got stuck in the slide system. There is a chance that adding paint and sanding would make the slides slippery enough so this didn’t happen, but I suspect I would have needed to do some minor tweaks to the slide system. By tweaks I mean change slide positions and angles.

4) I hadn’t hooked up the servos so I don’t know if there would have been a problem with selecting a single card. My hunch is that there would be a problem here and I’m not sure of an easy way to solve this one. My best bet would be buying those slightly thicker plastic cards.

I just saw orv’s comment. Your plan agrees with mine :) I do have a way to detect a specific spot on the card. The third gate stops the card at the same spot every time. The only variance is that the card can be face up/down and that it can be backwards/forwards. Since the borders are usually symmetric the backwards/forwards part doesn’t matter.

i dont see much hope for this project for a couple of reasons. Most importantly, visually interesting != random. I remember when the first auto shufflers (using elevators and motorized wheels to flip cards from two stacks into a center stack, which could then be cut split and re-shuffled). They had nice glass fronts so you could see the action — for a few weeks. Then someone figured out that if you aimed a hidden camera at it during the shuffle you could gather enough info about the shuffle to profitably track it. End of glass windows.

Second, the air shuffler just isn’t going to work with cards no matter what you do; it works with lottery balls because they don’t stick together or to surfaces, but cards do — and the more air you put on them, the harder they’ll be pushed against the walls and each other to form vacuum bonds. They will also fall into the separator in at a totally crazy array of angles which will jam half of them no matter how perfectly the chutes are made. (And making the chutes too perfect and smooth isn’t a solution, because that makes the vacuum bond situation worse.)

The way to pick a single sheet or card is not through thickness (which can vary during play as the cards get bent or swell due to humidity) but through friction. You need a rubber or polyurethane drive wheel on the bottom of the deck to drive one card when desired. You need fixed friction to prevent the other cards from following the first, usually an adjustable stationery rubber wheel about a card’s thickness from the bottom. Finally, if gravity isn’t enough you may want a spring follower on the top to keep feeding the cards to the bottom drive wheel.

There’s no good way to draw that in ASCII art, so I won’t try. But it’s how things like envelope feeders or other automated machinery deal with thin flat materials.

just to toss out an idea, how about a plinko style randomizing system. It’d be a pain to build something precise enough to have a precise 50% chance of going left or right, but at the end if built correctly should have the same orientation. there’s probably a statistical weakness for a fresh deck to hmm..

If you keep the shuffle chamber to a thickness less than the width of a card they can tumble but not flip so they wouldn’t need the sorting stage.
I would use a tumble box with a few odd shaped sides and or or random placed pegs to add to the random dispersion.

I was thinking that a brush like gasket to let one card might work and have a roller wheel on the underside. You may want to get those nice plastic cards as they are more durable. I this contraption with my suggestion as as is could causing marks on the cards which may be detrimental to a poker game as you could spot cards. Some teflon rails may be soft enough or drill small holes in the ramps and let some air into chambers to let the cards ride on a cushion of air.